1. Field of the Invention
This invention relates to an underground mine roof support and system adapted to follow an advancing mine face in a shortwall mining operation to protect personnel and equipment from roof falls while providing ready access to the face by mining equipment.
2. Description of the Prior Art
In mining operations such as the continuous mining of coal, no one prior to the present invention has successfully solved the problem of temporarily supporting the freshly-cut top or roof of a mine room just behind a continuous miner. Typically, about twenty feet of the top immediately outbye of the face is inaccessible to a roof bolting machine because the continuous miner and the shuttle car loading coal from it are in the working place. As a consequence, the miner must be moved to the next working place available, while a roof bolting machine moves into the freshly-cut place to install the required number of bolts. Further, though the miner itself is capable of operating continuously, it actually operates less than full-time in a conventional mining operation because of delays involved in moving from place to place and roof bolting.
Mining equipment and the labor to operate it are very expensive. Ideally, such equipment should be kept running all the time to minimize the cost per ton of mined material. Much effort has been spent in attempting to develop temporary roof support above a mining machine which will advance with a miner and enable it to operate continuously without down time to roof bolt on reset timbers. Some walking roof supports which have been proposed for this purpose are illustrated and described in U.S. Pat. Nos. 2,795,935; 2,795,936; 3,890,792; 4,129,990; and 4,143,991. None has been entirely satisfactory. The most recently publicized attempt to solve this problem has been based on the above U.S. Pat. No. 4,143,991, reported at pages 50-61 of the June, 1979 issue of "Coal Age". It had a series of individually movable transverse bars engagable with the roof. Although several prototypes of this machine have been made and tested, it is understood that several unsolvable problems developed, some of which were inherent in the design. Serious problems were the inability to turn cross-cuts, and to turn corners when making breakthroughs from one room to another.
Another problem in the design shown in U.S. Pat. No. 4,143,991 was permanent deformation of the roof support bars each of which extended completely across the room in one piece with no intermediate support. Further, the fixed width of the roof-engaging bars must be two feet or so less than the full width of the room itself to accommodate room neck-downs.